Fatphobia, as a structural and institutionalized form of discrimination, compromises the provision of equitable and inclusive healthcare for larger-bodied individuals, even within Brazil’s Unified Health System, founded on principles of universality and equity. This mixed-methods study was conducted with 387 health professionals working in Primary Health Care (PHC) units in Fortaleza, Brazil. Quantitative data were collected using the Fat Phobia Scale and the Beliefs About Obese Persons Scale, and analyzed using descriptive statistics and multiple linear regression. Qualitative data were collected via open-ended questionnaires and analyzed using Descending Hierarchical Classification and similarity analysis, with the support of the IRaMuTeQ software for lexical and textual statistical processing. Older age (≥ 40 years), self-rated poor/fair health, and Black racial identity were significantly associated (p < 0.05) with lower fatphobic attitudes and weaker beliefs in the individual controllability of body weight. Despite some recognition of the term “fatphobia”, most participants conceptualized “obesity” through a biomedical lens, emphasizing individual behavior and pathologizing fat bodies. Qualitative analyses revealed a superficial understanding of fatphobia, often detached from structural critique or professional practice. Behavioral change strategies remained central in treatment approaches, with limited awareness of sociopolitical determinants of body size. Fatphobia is pervasive among PHC professionals and is perpetuated by a dominant weight-centric paradigm rooted in biomedical education and social norms. There is a critical need for training and public health policy reforms grounded in fat studies and committed to equity, to foster inclusive care and challenge stigma across all body types.